[119.05] HST Observations of Gamma-ray Bursts

K. C. Sahu (STScI)

Two recent GRBs, GRB 970228 and GRB 970508, were observed
with the Hubble Space Telescope. HST observations of
GRB 970228 confirmed the association of GRB970228 with a
possible host galaxy and showed that the
GRB is situated off-center in the galaxy. This suggests
that GRBs are probably not related to nuclear activity.
The observations taken more than 200 days after the
outburst showed no movement of the GRB, no fading of the
extended component, and confirmed that the optical decay
behaviour continued until such late times. This places
strong contraints on the energetics of the gamma-ray
burst, and further suggests a cosmological origin
of the gamma-ray burst. HST observations of GRB970508,
on the other hand, did not reveal any host galaxy.
The observations show that any underlying galaxy must
be fainter than R 25.5 which, coupled with its observed
redshift of >0.8, indicates that the host galaxy
must be at least 10 times fainter than L*.
The implications will be discussed.

The author(s) of this abstract have provided an email address for comments about the abstract: ksahu@stsci.edu